The transition from analog electronics to digital electronics has caused sweeping technological changes within telecommunications and electronic instrumentation industries. For example, as clock-speeds in digital circuitry increase, so do the challenges in maintaining signal integrity with respect to adjacent signals interfering with one another. Other driving forces, that have also created technical challenges, are the demand for miniaturization of electronic devices and the demand for increasing the number of discrete functions associated with each electronic device. The latter two driving forces results in the packing of multiple electronic functions within a smaller cabinet volume, i.e., within a smaller surface space on a printed circuit board (PCB) within the cabinet dimensions. The limited PCB surface space requires closer component spacing that can result in components electrically interfering with or being influenced by neighboring components. For example, the phenomenon of antenna and receiver (crosstalk) is well known in the art.
More specifically, older connector designs were based on the use of low frequency signals using relatively high voltage and steady state current levels in which the flow of the energy was evenly distributed over the total cross-section of a conductor. A result of the effective impedance to the flow of such energy was electrical resistance. By contrast, contemporary digital signals operate at much higher frequencies with signal amplitudes in the micro-volt level. With such high frequency signals, transmission of energy migrates to the outer "skin" of the conductor and can be transmitted. Consequently, the impedance of the interconnect becomes an important design parameter.
In recent years, equipment designers and users have become more sensitive to the problems raised by increases in clock speed (frequency) and miniaturization. To alleviate these problems, there has been a gradual design shift towards coaxial or pseudo-coaxial shielded components.
New connector designs provide shielded interconnects with characteristics that allow propagation of high speed signals while reducing cross talk. In such interconnects, the electronic signal element, i.e., the connector terminal path, is preferably enclosed by an equi-spaced air annulus bounded by a metal shield, air being a preferred dielectric.
Optimum coaxial performance is achieved by a cylindrically shaped connector having a minimum of cross-section change over the length of the interconnect. In such a connector, the distance between the center conductor and the shield preferably will be uniform over the length of the connector. Unfortunately, round, coaxial connectors are typically machine-turned and expensive to manufacture.
Other types of shielded connectors, are substantially rectangular in shape, as a result of stamping. Connectors assembled with stamped components are easier and more cost-effective to manufacture. Generally such stamped structures typically include rectangular-shaped internal contact terminals.
Shielding such rectangular components requires an equi-spaced dielectric annulus. By the very fact that the shield structure is rectangular, rather than circular, there is a natural deviation with respect to ideal coaxial shielding. The performance of such shielding is less optimal than that of the ideal coaxial shielding and is, therefore, referred to as pseudo-coaxial.
Right angle or horizontal connectors are commonly used for many backplane applications. Not uncommonly, such right angle connectors, are designed to be press-fit to a printed circuit board and contain multiple rows and columns. In manufacturing such connectors, the contact terminals are stitched into a housing after which the back end of the terminal, known as the tail, is bent. Such bending is usually done row by row. The disparity in tail length between each row causes a difference in the impedance path for adjacent terminals. The resultant cross-talk from the tail section of such a connector is approximately 30 to 35% of the total crosstalk for the mated connector. A significant part of the cross-talk is attributed to the close spacing of the contact terminals.
Hence, there still exists a need to design a right-angle connecter having reduced size without sacrificing shielding performance for high frequency signals.